The first climate refugees
It’s unseasonably warm for Maine
as the Helmuth lab pull on their boots and foul weather pants. Drills, transect tapes, drones, laser levels, and more make their way out of the cars and into the intertidal under the rising sun. A team of eleven—professors and students, both graduates and undergraduates—are climbing over the slick algae-covered rocks to answer a question, how will populations of intertidal species change as the climate warms?
It’s the third week of May, 2017, and it’s the warmest of the year already. Temperatures, in Schoodic, Maine climbed to 92°F, a full twenty-seven degrees above the historical average *. Boston broke a record set in 1936, reaching the same 92°F on the 18th of May †. This makes for more comfortable fieldwork conditions up in Maine, where it can easily be frigid and raining, but the extreme heat also tips the cards to show a frightening future.
The Gulf of Maine stretches from the northern side of Cape Cod up to Nova Scotia. It is a body of water that has experienced intense human use, from early American whaling to the collapse of the cod fishery. Today, the Gulf of Maine is one of the fastest warming bodies of water on the planet, experiencing an average sea-surface temperature three degrees celsius higher than the climatological average ‡. The Gulf of Maine also experiences some of the largest swings in water temperature in the world, with the southern end reaching the seventies in late summer and freezing in some areas in the winter §.
Species living in the Gulf of Maine, are hardy, therefore, and withstand strong swings in temperature every year. Climate change, however, has already led to changes in the range of some species. Take the blue mussel (Mytilus edulis), a commercial species, and one that inhabits much of the coast of the Gulf of Maine. The southern edge of its range has already contracted as waters warm. Maine fishermen have reported a forty-seven percent decline in landings from 2003-2013 ‖, ¶. Commercial fish species have also exhibited range shifts and the spread of invasive species and disease have also increased.
This group of scientists intends to find out how temperature in the intertidal is influencing these populations. Led by Dr. Brian Helmuth, they focus on forecasting the effects of climate on marine organisms. This project is focused on an emerging complexity with climate change: the broad scale effects of climate change are felt differently in different environments by different organisms. That is, climate change doesn’t affect all organisms equally. Some species in an area may get away with living in a changed world, while some may be wiped out of an ecosystem. Even within an area, some individuals may be shaded from the sun or sheltered from a storm.
Helmuth and Northeastern have developed ways to predict the effects of temperature on a complex environment such as the Maine coast, where rocks and algae provide refuge from intense heat waves, where most of the damage is done by direct sunlight. The lab uses drones to map the rough landscape of the intertidal, allowing them to then model the shaded areas and predict how resilient an area is to heat stress.
The organisms hiding in these rocks are poised to become vital in the face of climate change. As severe weather such as heat waves increase, populations of intertidal creatures such as mussels could experience extreme decline. Mussels in shaded environment are protected from the heat and can therefore act as refugees, repopulating the area after an extreme event.
By this logic, more topographically complex areas could be more resistant to extreme climate events, with the pockets of survivors serving as seeds to replenish the surrounding populations. Generations of survival in these areas could favor the genetics of these survivors and have broad implications on distribution of species, with the dispersal of the new generations limited to these oases as sources.
Extreme climate events will surely have profound impacts on the oceans in the coming years. Understanding these complex effects is key to solving the problems that are sure to come. As temperatures increase, more commercial species will experience changes in range, and the people that rely on them for food and livelihood will be left high and dry. Being able to protect areas that we know will be able to kickstart recovery of devastated populations may help to minimize the damage done.
‡ Mills, K. E., A. J. Pershing, C. J. Brown, Y. Chen, F.-S. Chiang, D. S. Holland, J. A. Nye, S. Lehuta, J. C. Sun, A. C. Thomas, and R. A. Wahle. 2013. Fisheries management in a changing climate: Lessons from the 2012 ocean heat wave in the Northwest Atlantic. Oceanography 26:191-195.
§ Weare, B. C., and R. E. Newell. 1977. Empirical orthogonal analysis of atlantic ocean surface temperatures. Quarterly Journal of the Royal Meteorological Society 103:467–478.
‖ Jones, S. J., F. P. Lima, and D. S. Wethey. 2010. Rising environmental temperatures and biogeography: poleward range contraction of the blue mussel, Mytilus edulis L., in the western Atlantic. Journal of Biogeography 37:2243–2259.
¶ Jones, S. J., N. Mieszkowska, and D. S. Wethey. 2009. Linking thermal tolerances and biogeography: Mytilus edulis (L.) at its southern limit on the East Coast of the United States. Biological Bulletin 217:73-85.